WASHINGTON (CNN) -- The United Nations' top two weapons experts said Sunday that the invasion of Iraq a year ago was not justified by the evidence in hand at the time.

"I think it's clear that in March, when the invasion took place, the evidence that had been brought forward was rapidly falling apart," Hans Blix, who oversaw the agency's investigation into whether Iraq had chemical and biological weapons, said on CNN's "Late Edition with Wolf Blitzer."

Blix described the evidence Secretary of State Colin Powell presented to the U.N. Security Council in February 2003 as "shaky," and said he related his opinion to U.S. officials, including national security adviser Condoleezza Rice.

"I think they chose to ignore us," Blix said.

Mohamed ElBaradei, director general of the International Atomic Energy Agency, spoke to CNN from IAEA headquarters in Vienna, Austria.

ElBaradei said he had been "pretty convinced" that Iraq had not resumed its nuclear weapons program, which the IAEA dismantled in 1997.

Days before the fighting began, Vice President Dick Cheney weighed in with an opposing view.

"We believe [Iraqi leader Saddam Hussein] has, in fact, reconstituted nuclear weapons. I think Mr. ElBaradei, frankly, is wrong," Cheney said. "And I think if you look at the track record of the International Atomic Energy Agency in this kind of issue, especially where Iraq's concerned, they have consistently underestimated or missed what Saddam Hussein was doing."

Now, more than a year later, ElBaradei said, "I haven't seen anything on the ground at that time that supported Mr. Cheney's conclusion or statement, so -- and I thought to myself, well, history is going to be the judge."

No evidence of a nuclear weapons program has been found so far.

Blix, who recounts his search for weapons of mass destruction in his book "Disarming Iraq," said the Bush administration tended "to say that anything that was unaccounted for existed, whether it was sarin or mustard gas or anthrax."

Blix specifically faulted Powell, who told the U.N. Security Council about what he said was a site that held chemical weapons and decontamination trucks.

"Our inspectors had been there, and they had taken a lot of samples, and there was no trace of any chemicals or biological things," Blix said. "And the trucks that we had seen were water trucks."

The most spectacular intelligence failure concerned a report by ElBaradei, who revealed that an alleged contract by Iraq with Niger to import uranium oxide was a forgery, Blix said.

"The document had been sitting with the CIA and their U.K. counterparts for a long while, and they had not discovered it," Blix said. "And I think it took the IAEA a day to discover that it was a forgery."

Blix said that during a meeting before the war with the U.S. president, Bush told him that "the U.S. genuinely wanted peace," and that "he was no wild, gung-ho Texan, bent on dragging the U.S. into war."

Blix said Bush gave the inspectors support and information at first, but he said the help didn't last long enough.

"I think they lost their patience much too early," Blix said.

"I can see that they wanted to have a picture that was either black or white, and we presented a picture that had, you know, gray in it, as well," he said.

Iraq had been shown to have biological and chemical weapons before, "and there was no record of either destruction or production; there was this nagging question: Do they still have them?" ElBaradei said.

Blix said he had not been able to say definitively that Iraq had no such weapons, but added that he felt history has shown he was not wrong.

"At least we didn't fall into the trap that the U.S. and the U.K. did in asserting that they existed," he said.

ElBaradei faulted Iraq for "the opaque nature of that Saddam Hussein regime."

"We should not forget that," he said. "For a couple of months, their cooperation was not by any way transparent, for whatever reason."

ElBaradei said he hoped the past year's events have taught world leaders a valuable lesson.

"We learned from Iraq that an inspection takes time, that we should be patient, that an inspection can, in fact, work."